The present invention relates to pneumatically driven apparatus and, in particular, to pneumatically driven hand tools, construction methods, and the channeling of air through these tools.
Pneumatic hand tools, such as air grinders, are well known. Typically, these hand tools have an elongated housing with a handle portion at one end and a collet or arbor for mounting various types of abrasive media at the other end. An air motor is typically disposed in the housing intermediate the ends for driving the arbor, the air motor being coupled to a source of pressurized air through a fluid inlet which commonly extends axially through the handle portion. The housing may be provided with a trigger, which may be in the form of a lever alongside the outside of the housing or a radially projecting button, adapted to be operated by a finger or fingers of the user's hand which grasps the handle, for operating an internal valve to admit air to the air motor.
In prior air tools, various types of exhaust arrangements have been utilized. In one arrangement the air is exhausted from a forward portion of the housing to clean the working area, for example. Commonly, the air exits the air motor into a circumferential passage or chamber, which may contain a muffler arrangement and communicates with an exit opening at a forward portion of the housing. Alternatively, rear-exhaust arrangements have also been utilized, which include an exhaust passage, which passes back through the handle portion, generally parallel to the inlet passage.
To provide these different exhaust arrangements, some conventional tools use a reversing valve mechanism to reverse the flow of exhaust fluid, which increases both complexity of construction and cost. Other known tools are constructed solely for front exhaust or rear exhaust, which require the manufacture of different parts for conversion between alternate exhaust configurations. In addition to reversing exhaust air direction, it is desirable to vary motive fluid flow through a motor construction to obtain different motor speeds for the same motor construction. Typically this can be done by sizing and shaping an orifice in the fluid flow path to restrict fluid flow to a predetermined mass rate of flow, thus limiting motor speed. This speed regulation can be accomplished with a variable regulating valve or, alternatively, with many single use permanent parts. Variable regulating valves typically are complex and subject to wear while single use permanent parts reduce the flexibility of converting the tool and create logistical problems in manufacturing the various parts. Both alternatives are typically costly to construct.
The construction of these pneumatic hand tools is typically accomplished by assembling components into an outer housing made of a thermoplastic such as an injection molded nylon or other plastic material. During assembly, these materials can be subject to breakage due to excessive holding forces that can be caused by holding the housing in a vise or other jig configuration.
The foregoing illustrates limitations known to exist in present pneumatic devices. Thus it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly an alternative assembly construction, pneumatic flow guide and apparatus incorporating the same are provided including the features more fully disclosed hereinafter.